In many industries producing flat end-products, e.g. paper, steel and other metals, flat-sheet chemicals like polymers and film industries, the entire production process is monitored. The quality of the process is measured using on-line measurement and control systems, such as quality control systems, scanning the strip-like material continuously or using imaging systems, providing full strip imaging of the quality and defect data.
This quality and defect information is typically used to control the production process itself. During the production process, the flat product may stretch or shrink, and in addition to this there are typically length direction losses, slabbing, that take out some material on top or in the middle of the reel. As a result of all these changes in the length at each of the processing steps, the current positions of quality and defect data in the reel is typically not known exactly.
One of the final processing steps of flat end-products is cutting. The main reason for postponing the cutting step towards the end of the production is that this allows the simultaneous processing of larger quantities and the design of more generic production equipment that do not depend on certain individual end-product dimensions. Determining a cutting plan faces the following difficulties: how to match the product dimensions required by the customers to those of the equipment and how to group end-customer products according to their material property and quality requirements and how to minimize the wastage of the material to be cut. This problem is referred to as the trim-loss problem or cutting stock problem.
In the cutting process a wound up product, a reel or a coil, is cut into smaller products. This is done using special slitting devices and suitable winding systems. What it means in practice is that a larger unit will be divided into smaller units, after which further processing or packaging takes place. The end-products can be wound up in rolls, machine direction cutting, or cut into sheets, machine and cross direction cutting.
Because of the quality and defect variations in the reel or coil to be cut and their inaccurate position information, it may happen that a cut customer roll that is thought to be of perfect quality ends up having severe defects in it.
In the case of a paper roll this would in the worst case lead to customer rejects at the printing house, as the product sold as premium is actually of poor quality. The customer claims cause financial costs through penalties and extra transportation and handling needed. In addition to these, even more severe effect may be the end customer switching suppliers due to the poor quality.
These losses due to in-accuracies may be up to several percent of the total production capacity, thus making their financial impact to the profitability of the production process significant.